1. Field of the Invention
The present invention relates to a map data distribution system for distributing map data through a network and to a navigation apparatus for receiving distributed map data and for performing navigation operations such as displaying a map and the like.
2. Description of the Related Art
In general, in-vehicle navigation apparatuses have various functions, such as a map display function for displaying a map around the position of a vehicle on a display screen, a route search function for searching for a route to a destination designated by a user, a route guidance function for guiding the vehicle to travel along the route found by the route searching, and a point-of-interest (POI) information function for displaying symbols showing various points of interest at positions on the map and for displaying information relating to the points of interest. Normally, predetermined processing is performed using map data provided through a disc medium, such as a digital video disc (DVD) or a compact disc (CD), in order to realize such functions.
The content of the map data described above is appropriately updated by a particular manufacturer or the like that produces and maintains the map data, so that the map data reflects the latest road information. Although the updated map data can be obtained by purchasing the latest DVD or the like, downloading only an updated part of the map data through a communication link is also possible these days.
In the conventional system for obtaining updated map data through a communication link, a predetermined unit of map data is prepared by a map distribution server that provides map data and is distributed. Thus, users of the navigation apparatuses cannot always obtain map data under distribution conditions desired by the users. For example, map data for update is prepared for each map section created by dividing by predetermined latitude and longitude. Each piece of map data for update is transmitted in accordance with a distribution instruction from the navigation apparatus. As a result of this, distribution may need a longer time than the users expect and unnecessary map data corresponding to areas not required by the users may be distributed. The map data includes different types of data, such as map image data, road data, and point-of-interest (POI) data. Even if a user desires to obtain, for example, only the latest map image data, the road data and the POI data included in the same map section are also transmitted. Therefore, the user needs to spend time and money for receiving all the data included in the same map section.